Is there any reason to think that vulcans and humans need genetic engineering to mate? Lorian from Enterprise was a hybrid and he was the child of a human and a vulcan on a 22nd century starship without any mention of any help. We also had Sela and Simon Tarses, who were Romulan/Human and again, no mention of genetic engineering. Hell, Klingon/Trill was even possible, just with a few weeks worth of research by one doctor.